Fastener driving tools, also known as impulse tools, have been developed that use internal combustion as a power source to drive fasteners such as nails into a work piece or substrate. The tools ignite a fuel/air mixture in a combustion chamber to forcibly drive a piston, which then ejects the fastener from the tool. The effectiveness of the prior art is largely limited to their efficiency in rapidly igniting the complete volume of fuel/air mixture. If insufficient volumes of fuel ignite, the device delivers unsuitable driving forces to the fastener. If the tool produces unreliable power outputs the fasteners may be driven to unsatisfactory depths or insufficiently seated. Prior art devices have attempted to address these inefficiencies by making a larger tool and wasting larger volumes of fuel.
Some prior art tools also suffer from what is known as misfire or non-fire. This occurs when the tool is operated in low temperature conditions or at high altitude and hot conditions. The cause of the phenomenon is; (a) insufficient atomization and mixing of the air/fuel; (b) an insufficient fuel/air ratio; (c) low air density.
One such prior art tool is described in U.S. Pat. No. 5,213,247 (Gschwend et al). This device includes a network of mechanisms that operate to measure a specific quantity of fuel and then draw that fuel, along with air, into a combustion chamber by mechanically expanding the combustion chamber volume. A drawback of this device is that the fuel and gas are not mixed sufficiently, which decreases the efficiency of combustion.
A further disadvantage of such prior art tools is the tool mass (weight and physical size) required for a given output of energy. Furthermore, such tools draw fuel and air into the combustion chamber with partial vacuum. As a consequence the fuel/air mixture is ignited at a low pressure, which leads to a low burn rate and further inefficiency. This is particularly problematic in that the less efficient an internal combustion fastener driving tool is, the more susceptible the device is to output fluctuations that result in ignition failures and unsatisfactory driving forces to the fastener.
Also prior art impulse tools such as those used in nail and fixing in the building industry have limitations in their use. Such tools have the capability of producing 70 to 100 joules of output energy. These tools will only produce their manufactured claimed output under optimal conditions ie; 24C @ sea level and a relevant humidity level of approximately 40%. If these optimum conditions change, so does the power output by as much as 25%, and in some cases they do not fire at all. This means that nails and fixers sometimes protrude and are only driven 80 to 90% of the manufactured depth, and thus the work piece may not meet building standards. This may also lead the operator to have to use a traditional hammer to finish the job.
Some impulse tool manufactures have developed tools to produce in excess of 100 joules, but such tools have ended up being a far larger unit for consumers to reasonably expect to purchase.
All prior art combustion tools used for fixing, suffer from gumming up and need to be cleaned regularly. This is caused by incomplete combustion in the tool. Carbon, lubricants and other bi-products of combustion and exhaust gases build up deposits within the combustion chamber, driver piston and head.
The present invention seeks to provide a fastener driving tool that will ameliorate or overcome at least one of the deficiencies of the prior art.